ECMWF atmospheric data sets

ERA-40 re-analysis (1958 - 2001)
Covering more than four decades from 1957 until 2001, the ECMWF re-analysis ERA-40 (Uppala et al. 2006) provides 6 hourly analysis data which are available on 23 pressure levels with 1.25° horizontal resolution. Although the re-analysis was intended to provide a homogeneous data set suitable for climate studies, spurious trends and changes in variability have been detected in various key quantities, including middle atmosphere dynamics (Randel et al., 2009), the hydrological cycle (Hagemann et al.,2005), and atmospheric mass transports (Graversen, 2007).

ERA Interim (since 1989)
Substantial improvements of the physical model and the data assimilation techniques led recently to a new re-analysis effort. ERA Interim (Uppala et al., 2008) has been produced since 1989 and is expected to be updated sequentially with latencies of a few months. The data used here at GFZ is distributed on 37 pressure levels with a horizontal resolution of 1°. Compared to ERA-40, the long-term homogeneity of ERA Interim has been significantly improved. Excessive precipitation in the tropics has been largely reduced, although it still remains higher than observational estimates. The Brewer-Dobson circulation is more reasonable now, and biases in wind speed over the extra-tropical oceans are less distinct. The annual cycle of specific humidity is much smaller than in ERA-40, in particular the transports across the tropopause are reduced (Uppala et al., 2008).

operational ECMWF data (used since 2001)
In addition to the re-analysis data, which is typically available with latencies of months to years, operational ECWMF data is considered as well. The operational model is subject to ongoing developments intended to continuously improve the weather forecast accuracies. Upgrades of the operational model usually take place two to four times a year, including for example changes in model physics, changes in observation handling or the introduction of improved data assimilation algorithms. The current model version runs on a T799 grid (approximately 25km horizontal resolution) with 91 vertical levels. The data is currently provided on 25 pressure levels, and a horizontal resolution of 1° is used for the products provided on this site.

ECMWF short-term forecasts (used since 2003)
Operational forecast runs covering 10 days with up to 3 hours temporal resolution are carried out by ECMWF two times a day. Products provided at this site are based on data-sets with horizontal grid-spacing of 1° that are discretized on 25 pressure levels. For the calculation of EAM forecasts, only forecast runs starting at 12 hours UTC are considered.


References:  

• Graversen, R.G., Källen, E., Tjernström, M., and H. Körnich (2007), Atmospheric mass-transport inconsistencies in the ERA-40 re-analysis, Q. J. Roy. Meteor. Soc., 133, 673-680.
• Hagemann, S., Arpe, K., and L. Bengtsson (2005), Validation of the hydrological cycle of ERA-40, ERA-40 project series, 24, European Centre for Medium-Range Weather Forecasts, Reading, U.K.
• Randel, W.J. et al. (2009), An update of observed stratospheric temperature trends, J. Geophys. Res., 114, D02107.
• Uppala et al. (2006), The ERA-40 re-analysis. Quart. J. R. Meteorol. Soc., 131, 2961-3012.
• Uppala, S., Dee, D., Kobayashi, S., Berrisford, P., and A. Simmons (2008), Towards a climate data assimilation system: status update of ERA Interim, ECMWF Newsletter, 115, 12-18.